Alkylation is typically used to combine light olefins, for example mixtures of alkenes such as propylene and butylene, with isobutane to produce a relatively high-octane branched-chain paraffinic hydrocarbon fuel, including isoheptane and isooctane. Similarly, an alkylation reaction can be performed using an aromatic compound such as benzene in place of the isobutane. When using benzene, the product resulting from the alkylation reaction is an alkylbenzene (e.g. ethylbenzene, cumene, dodecylbenzene, etc.).
The alkylation of paraffins with olefins for the production of alkylate for gasoline can use a variety of catalysts. The choice of catalyst depends on the end product a producer desires. Typical alkylation catalysts include concentrated sulfuric acid or hydrofluoric acid. However, sulfuric acid and hydrofluoric acid are hazardous and corrosive, and their use in industrial processes requires a variety of environmental controls.
Solid catalysts are also used for alkylation. However, solid catalysts are generally rapidly deactivated and may be prohibitively expensive.
Acidic ionic liquids have been used as an alternative to the commonly used strong acid catalysts in alkylation processes. Ionic liquids are essentially salts in a liquid state, and are described in U.S. Pat. Nos. 4,764,440, 5,104,840, and 5,824,832. The properties vary extensively for different ionic liquids, and the use of ionic liquids depends on the properties of a given ionic liquid. Depending on the organic cation of the ionic liquid and the anion, the ionic liquid can have very different properties. The most common ionic liquid catalyst precursors for alkylation include imidazolium or pyridinium-based cations coupled with the chloroaluminate anion (Al2Cl7−).
Ionic liquids provide advantages over other liquid catalysts, including being non-volatile.
Other hydrocarbon conversion processes, including isomerization, oligomerization, disproportionation, and reverse disproportionation, also use ionic liquid catalysts.
The hydrocarbon conversion reaction will proceed simply by contacting the hydrocarbon feed and the ionic liquid catalyst. The reaction is biphasic and takes place at the interface in the liquid state due to the low solubility of hydrocarbons in ionic liquids. The hydrocarbon feed and the ionic liquid catalyst are often mixed to produce smaller ionic liquid catalyst droplets and thereby increase the mass transfer resulting in an increased reaction rate.
However, there is a need to control the mass transfer resistance in the reactor to control the reaction product.